Bloody Sunday memorial

Saul Loeb, AFP/Getty Images

President Barack Obama, first lady Michelle Obama, former President George W. Bush, former first lady Laura Bush and U.S. Rep. John Lewis lead a walk across the Edmund Pettus Bridge on March 7, 2015, to mark the 50th anniversary of civil rights marches in Selma, Ala.

President Barack Obama, first lady Michelle Obama, former President George W. Bush, former first lady Laura Bush and U.S. Rep. John Lewis lead a walk across the Edmund Pettus Bridge on March 7, 2015, to mark the 50th anniversary of civil rights marches in Selma, Ala. (Saul Loeb, AFP/Getty Images)

President Barack Obama, first lady Michelle Obama, former President George W. Bush, former first lady Laura Bush and U.S. Rep. John Lewis lead a walk across the Edmund Pettus Bridge on March 7, 2015, to mark the 50th anniversary of civil rights marches in Selma, Ala.